static L<S> dropPunctuationAtEnd_hard(L<S> tok) {
  tok = new ArrayList<S>(tok);
  for (int i = tok.size()-2; i > 0; i -= 2) {
    S t = tok.get(i);
    if (t.length() == 1 && !Character.isLetterOrDigit(t.charAt(0))) {
      tok.remove(i);
      tok.remove(i);
    } else break;
  }
  return tok;
}

static S dropPunctuationAtEnd_hard(S s) {
  ret join(dropPunctuationAtEnd_hard(nlTok(s)));
}